Manually-controlled rate meters are commonly used to control the flow of materials, particularly liquids, through a system. One example of a system in which rate meters are utilized is a sprayer system in agricultural implements which apply fertilizers, pesticides, herbicides, and other agricultural chemicals ("agents") to fields.
One agent that has proven especially difficult to control with a manually-controlled rate meter is anhydrous ammonia (NH3). Nevertheless, commercial farmers have increasingly relied on applications of anhydrous ammonia as a source of nitrogen for their crops. Anhydrous ammonia is stored in a pressure vessel or nurse tank in its liquid form due to its own vapor pressure at its boiling point. Since anhydrous ammonia, as a liquid under pressure, vaporizes at approximately 28.degree. F., it is difficult to measure and control.
A common sprayer system application of anhydrous ammonia is accomplished by a tractor pulling a tool bar with at least one manually-controlled rate meter for metering the flow of anhydrous ammonia into a plurality of knifed injectors. The tool bar is attached to a nurse tank housing the anhydrous ammonia and has connections to the nurse tank that allow the flow of anhydrous ammonia from the nurse tank through the manually-controlled rate meter on the tool bar.
The vapor pressure in the nurse tank provides the energy to move the anhydrous ammonia through the system. As liquid anhydrous ammonia moves through the system it experiences a pressure drop which results in a temperature drop and more vapor. The pressure drop, which causes vaporization, decreases the energy available to move the anhydrous ammonia, resulting in a lower application rate. In addition to vapor pressure changes, the application rate is also affected by changing vehicle speeds. When the vehicle moves faster, the same amount of anhydrous ammonia is applied over a larger area. When the vehicle slows down, the same amount of anhydrous ammonia is applied over a smaller area.
The lack of effective control of the application of anhydrous ammonia or other agents because of changing vehicle speed and changing system pressures results in either an over-application or an under-application of the agent. This can cause substantial reductions in crop-yields.
Several fully integrated metering control systems currently exist that allow for automatic compensation for speed and pressure changes. Examples of such devices include U.S. Pat. No. 5,170,820 issued to James S. Jones and U.S. Pat. No. 4,458,609 issued to David S. Tofte. U.S. Pat. No. 5,170,820 uses a throttling device, a ground speed sensor, an ammonia flow reader, and hardware that interfaces with existing microprocessors on the vehicle to send control signals to adjust the throttling device for controlling the application rate of anhydrous ammonia based on the sensed ground speed and sensed flow rate. U.S. Pat. No. 4,458,609 uses a heat exchanger attached to a flow control valve, a flow sensor and a control console, with automatic controls that can be responsive to the ground speed of the vehicle and the sensed flow rate of the anhydrous ammonia, for sending control signals to adjust the valve to the desired application rate of anhydrous ammonia.
Although these inventions address the problems encountered by an apparatus that uses manually controlled rate meters, they require replacement of the existing applicator equipment or extensive plumbing changes to be made to the applicator apparatus, which can be quite expensive. They do not, therefore, provide a practical solution to those farmers that currently use applicators having manually operated rate meters which need a simple controller that does not require plumbing changes and that provides automatic adjustments to the manually operated rate meters while in operation.
Two commonly used manually controlled rate meters for anhydrous ammonia include meters manufactured by Continental and sold under model number C4100 and B9500. These manually-controlled rate meters attempt to maintain a constant pressure of the anhydrous ammonia as it flows through the system. However, the mechanical rate meters respond slowly to changing air temperatures, which cause changing tank pressures. Low air temperatures cause the pressure in the nurse tank to drop, resulting in less energy to move the anhydrous ammonia through the system and hence, a lower application rate. In addition, the rate meter offer no compensation for any fluctuations in vehicle speed result in an inconsistent application rate per ground area covered.
Application rates for the Continental Meters are manually adjusted by the operator, by moving an external rate meter control device, typically a rotary dial, to set the application rate to a desired level of nitrogen per hour. The operator determines the nitrogen level setting by using a preprinted chart that indicates the appropriate nitrogen setting based on the vapor pressure in the nurse tank and the anticipated speed at which the vehicle will be moving. Another manually operated rate meter as disclosed in U.S. Pat. No. 4,364,409 issued to James S. Jones, has a calibration dial to set the application rate to a predetermined level of anhydrous ammonia per hour based on a choice of two different vapor pressures.
Although operators can calibrate manually controlled rate meters to compensate for vehicle speed and vapor pressure prior to application, manually controlled rate meters respond slowly to varying ambient air temperatures. Furthermore, manually-controlled rate meters do not automatically compensate for varying vehicle speeds nor do they allow for changes to the application rate. While the application rate as set by the operator may be accurate under constant temperature and speed conditions, such ideal conditions are rarely present. Temperature and speed fluctuations are routine in agricultural applications. In order to keep the application rate consistent when using manually controlled rate meters, the operator must stop the vehicle and manually adjust the rate meter control device as the temperature changes or the speed changes.
In addition to the need for a simple controller that allows automatic control of manually operated rate meters, there is a need to integrate the controller with other agricultural control systems. Typically, farm implements are controlled by the operator of the agricultural vehicle to which the implements are attached or coupled. For example, planting and spraying systems have evolved for controlling and monitoring planting and spraying implements, respectively. As is detailed in U.S. Pat. No. 5,260,875 filed Aug. 20, 1991, issued Nov. 9, 1993, and assigned to same assignee, which is hereby fully incorporated by reference, these systems have for the most part evolved separately.
U.S. Pat. No. 5,260,875 details the shortcomings of prior art integrated agricultural control systems, stating that such control systems still require a separate planting controller for planting systems and a spraying controller for spraying systems. Before U.S. Pat. No. 5,260,875, mechanisms for the sharing of information gathered during each operation or the incorporation of shared information to improve implement control were generally not available. The separation of the two functions means that either individual passes must be made through a field for planting, fertilizing and pesticide application or the application vehicle must be cluttered with a multitude of incompatible controller equipment, each with its own unique calibration, maintenance and operational needs.
Furthermore, separate cables must be routed from each system component to its associated controller. The result is a jumble of wiring and reduced system reliability. Sensors that are to be used by more than one system must by necessity be connected to each system. As the types of sensors used in spraying and planting increase in number and the sensors become more complex, the information they generate could be profitably shared by many applications, but cannot be shared without further increasing the complexity, and potential misconnection and other wiring problems, of wiring.
The 5,260,875 patent addresses this perceived need by providing a distributed controller system which uses a half-duplex serial line as a bus that can be used to transfer commands, status and data between all controllers in a planting and spraying system. A bus master connected to the serial line synchronizes each controller to the network while a base console coordinates the operation of each planting and spraying system and presents a simple, uniform user interface. Separate system controllers operate in conjunction with system accessory modules to control the components of each planting and spraying system.
In such systems, communication and control cabling for the components is simplified by terminating such cables at accessory modules located close to the components herein controlled. Data related to each component is then transferred from the accessory modules to the controllers on the single serial line.
This separation of the accessory modules from their associated controllers provided in the 5,260,875 patent leads to efficient and logical system partitioning. Accessory modules can be placed in close proximity to the components they control while base and subsystem controllers are placed close to the user. The result is an integrated network of controllers for the monitoring and control of an agricultural planting and spraying system. A system can be partitioned into one or more planting, spraying and monitoring subsystems with each subsystem controlled by a subsystem controller. A half-duplex serial communications network connects the subsystem controllers to each other and to a base console which coordinates the user interface. A bus master synchronizes message traffic on the network by periodically sending a synchronizing message to the controllers. In operation, each subsystem controller monitors traffic on the network to determine when to read data on the network and when to drive data onto the network. Data present on the network can be read by more than one controller at a time. This simplifies the sharing of information present on the network. What is needed is a way to bring the integration of the above system to anhydrous ammonia spraying systems.